ORIGINAL ARTICLE INTRODUCTION

Transcription

1 Arthritis Care & Research Vol. 70, No. 10, October 2018, pp DOI /acr , American College of Rheumatology ORIGINAL ARTICLE Are Older Adults With Symptomatic Knee Osteoarthritis Less Active Than the General Population? Analysis From the Osteoarthritis Initiative and the National Health and Nutrition Examination Survey LOUISE M. THOMA, 1 DOROTHY DUNLOP, 2 JING SONG, 2 JUNGWHA LEE, 2 CATRINE TUDOR-LOCKE, 3 ELROY J. AGUIAR, 3 HIRAL MASTER, 1 MEREDITH B. CHRISTIANSEN, 1 AND DANIEL K. WHITE 1 Objective. To compare objectively measured physical activity in older adults with symptomatic knee osteoarthritis (OA) with similarly aged adults without osteoarthritis (OA) or knee symptoms from the general population. Methods. We included people ages years with symptomatic knee OA from the Osteoarthritis Initiative (OAI, n = 491), and ages years from the general population using National Health and Nutrition Examination Survey (NHANES, n = 449) data. A uniaxial accelerometer was worn for 10 hours/day for 4 days in the NHANES group in and in the OAI group in We calculated time spent in moderate-to-vigorous physical activity (MVPA in minutes/day) and described differences in MVPA and demographic variables between the samples. We conducted matched-pairs sensitivity analyses to further evaluate the role of potential confounders. Results. Both cohorts had similarly low levels of physical activity in age- and sex-specific strata. Time in MVPA ranged from a median of 1 22 minutes/day in people with symptomatic knee OA, and from 1 24 minutes/day in the general population without OA or knee pain. These results were similar in sensitivity analyses. Conclusion. Time spent in MVPA was similarly low in those with symptomatic knee OA as in older adults without knee pain or OA. INTRODUCTION Conventional wisdom suggests that persistent knee pain, a hallmark symptom of knee osteoarthritis (OA), hinders participation in physical activity. Indeed, people with knee OA perceive pain as a barrier to being active (1), and they selfreport participating in less physical activity than healthy adults (2 6). Yet more recent research using objectively measured physical activity shows mixed results and challenges the notion that people with knee OA are less physically active than the general population (7,8). Physical activity monitors (i.e., pedometers, accelerometers) provide objective, valid, and reliable measurement of physical activity frequency, intensity, and duration (9), allowing researchers to more precisely estimate physical activity relative to self-report questionnaires (10). Using This article was prepared using an Osteoarthritis Initiative (OAI) public-use data set, and its contents do not necessarily reflect the opinions or views of the OAI Study Investigators, the NIH, or the private funding partners of the OAI. The OAI is a public private partnership between the NIH (contracts N01-AR , N01-AR , N01- AR , N01-AR , and N01-AR ) and private funding partners (Merck Research Laboratories, Novartis Pharmaceuticals, GlaxoSmithKline, and Pfizer, Inc.) and is conducted by the OAI Study Investigators. Private sector funding for the OAI is managed by the Foundation for the NIH. The authors of this article are not part of the OAI investigative team. Supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (R01-AR , R21-AR , and P60-AR ) and by the Falk Medical Trust. Dr. White s work was supported by the NIH (U54-GM and K12-HD ). 1 Louise M. Thoma, PT, DPT, PhD, Hiral Master, PT, MPTh, MPH, CPH, Meredith B. Christiansen, PT, DPT, Daniel K. White, PT, ScD, MSc: University of Delaware, Newark; 2 Dorothy Dunlop, PhD, Jing Song, PhD, Jungwha Lee, PhD: Northwestern University, Chicago, Illinois; 3 Catrine Tudor-Locke, PhD, Elroy J. Aguiar, PhD: University of Massachusetts, Amherst. Address correspondence to Daniel K. White, PT, ScD, MSc, University of Delaware, STAR Health Sciences Complex, 540 South College Avenue, Suite 210L, Newark, DE dkw@udel.edu. Submitted for publication June 9, 2017; accepted in revised form January 2,

2 Physical Activity in Adults With and Without Symptomatic Knee OA 1449 Significance & Innovations This study uses large well-established cohorts to compare objectively measured moderate-to-vigorous physical activity in people with symptomatic knee osteoarthritis (OA) and people from the general population without OA or knee pain. Physical activity was similarly low in both cohorts. This study reiterates the pressing need to develop and implement successful interventions to increase physical activity in the general population and people with symptomatic knee OA, as the general population is doing as little as people with symptomatic knee OA. these more precise tools, how the physical activity levels of people with knee OA compare to the general population remains unclear. Small studies have directly compared physical activity in people with knee OA and healthy controls using objective measures (11 13). Synthesizing these studies, Wallis et al (14) estimated that people with knee OA are 75% as active as healthy controls. On the other hand, most studies objectively measuring physical activity in large populations of people with knee OA have not directly compared to a general population or healthy controls. Instead, these studies (5,7,8) have discussed their results relative to published epidemiologic studies of people from the general population that reported physical activity levels and the prevalence of meeting national guidelines for aerobic physical activity (10,15). In contrast to the smaller studies with direct comparisons, the results of the population-based studies concluded that the prevalence of meeting national physical activity guidelines for aerobic activity among people with knee OA was low (6 30%) (5,7,8), but similar to estimates in the general population (2 10%) (5,7,8,10,14,15). Larger data sets and intentionally defined groups will allow us to more confidently understand whether people with symptomatic knee OA are less active than people from the general population without knee OA or knee symptoms. Such an investigation is important, since knee OA is commonly perceived to be a barrier to physical activity (1). Moreover, investigating physical activity is important because inactivity is a global pandemic that contributes to the incidence and progression of many chronic diseases, including cardiovascular disease (16 19), diabetes mellitus (17 19), and cancer (19,20), and consequently is responsible for over 5.3 million deaths yearly (21). The purpose of this study was to compare objectively measured moderate-to-vigorous physical activity (MVPA) in older adults with symptomatic knee OA with similarly aged adults without knee symptoms or self-reported OA from the general population in the US. We hypothesized that those with symptomatic knee OA spend less time in MVPA than adults without knee symptoms or self-reported OA. We focused specifically on MVPA because it is the recommended intensity to meet national physical activity guidelines for aerobic activity (22). PATIENTS AND METHODS Sample. We used data from the OAI to describe physical activity in older adults (n = 491) with symptomatic knee OA. The OAI is a large multicenter prospective cohort study of individuals with or at risk for knee OA in the US. From 2008 to 2010, objective physical activity data were collected in a subset of individuals in the OAI in conjunction with the 4-year followup (from time of enrollment). Of this subset, we included people ages years who participated in the accelerometer study and provided at least 4 valid days of data. We excluded people without radiographic OA (Kellgren/Lawrence [K/L] grade <2) or no knee pain, aching, or stiffness on most days of a month during the previous year. We excluded people with asymptomatic radiographic knee OA because the symptoms associated with OA are generally expected to be the limiting factor for physical activity participation (1). This exclusion resulted in a sample of adults with symptomatic knee OA (Figure 1), defined as K/L grade 2 and the presence of knee pain, aching, or stiffness on most days of a month during the previous year. We used data from the National Health and Nutrition Examination Survey (NHANES) to represent physical activity in the general population of older adults (n = 449). NHANES has been administering a series of surveys regarding health and nutrition in a nationally representative sample of noninstitutionalized people across the country since In the and NHANES cycles, objective physical activity data were collected with accelerometers in a subset of the sample. We used data from the cycle because this cycle additionally included questions related to arthritis and joint pain. We included participants ages years who took part in the accelerometer study and provided at least 4 valid days of data (defined in data analysis). Participants from the NHANES were excluded if they self-reported OA or knee symptoms. Specifically, people with OA were identified as those who answered yes to the question Has a doctor or other health professional ever told you that you had arthritis? and indicated osteoarthritis as the type. Participants with knee symptoms were identified as those who pointed to the right or left knee during a personal interview asking which joints had pain, aching, stiffness, or swelling in the previous 12 months. Data collection. Demographic variables were collected with questionnaires and during examinations in both cohort studies. Age was recorded. Height was measured with a stadiometer. Weight was measured with a balance-beam scale in the OAI and a digital scale in the NHANES. Body mass index (BMI; kg/m 2 ) was calculated from height and weight. Race (white, African American, other), education level (less than high school, high school graduate, some college, college graduate), marital status (married, not married), income level (<$25,000, $25,000), and presence of comorbidity ( 1, none) were described as proportions within concordant response categories between the OAI and the NHANES questionnaires. Presence of comorbidity was defined as people who reported a history of or current heart attack, heart failure, stroke, emphysema, chronic bron-

3 1450 Thoma et al Figure 1. Flow chart describing how the analytic samples were derived from the full Osteoarthritis Initiative (OAI) and the National Health and Nutrition Examination Survey (NHANES) samples. KL = Kellgren/Lawrence; SxOA = symptomatic knee osteoarthritis; OA = osteoarthritis. chitis, chronic obstructive pulmonary disease, or asthma, because these cardiopulmonary pathologies potentially restrict participation in physical activity. Physical activity was measured in the NHANES and the OAI with an ActiGraph uniaxial accelerometer. The participants were instructed to wear the ActiGraph at the right hip during waking hours for 7 consecutive days. The NHANES used the ActiGraph 7164, whereas the OAI used the ActiGraph GT1M. In a direct comparison of these models during self-paced walking, Kozey et al (23) observed that time spent in higher-intensity categories (i.e., MVPA) and medium-speed walking were not different between models. Since our analysis was limited to higher-intensity activity (i.e., MPVA), potential bias due to different Acti- Graph models was minimized. Pain in the lower quarter other than the knee may also limit physical activity. To adjust for the existence of other pain, we identified people in each sample who reported lower-quarter pain, i.e., pain in the lower extremity or lowback pain. The knee was not included in the definition for lower-quarter pain since it was in the exclusion criteria for the study samples. In each data set, there were differences in the questions regarding lower-quarter pain, thus there were small differences in how lower-extremity pain was defined. For the OAI, the presence of lower-quarter pain was defined as reported ankle or foot pain on most of the last 30 days or hip pain on most days of 1 month in the last year, or low-back pain in the last 30 days. For the NHANES, the presence of lower-quarter pain was defined as people who reported hip or ankle pain in the last year, foot pain in the last month lasting >24 hours, or low-back pain in the last 3 months or lasting >24 hours in the last month. Data analysis. Accelerometer data from the OAI and NHANES were processed using the same methods and are consistent with processing of ActiGraph data in prior studies (7). A SAS macro provided by the National Cancer Institute (available at nes_pam) was used to determine ActiGraph wear time. Nonwear time was defined as 60 minutes of zero activity, with allowance for up to 2 minutes of activity counts 0 100, and subtracted from 24 hours to determine wear time (15). A valid wear day was defined as a day with 10 hours of wear time. Participants were included if 4 7 valid wear days were available, regardless of the day of the week. An MVPA minute was analytically identified by activity counts 2,020/minute (15). The primary variable of interest was average minutes/day spent in MVPA. Statistical analysis. The NHANES is a national probability sample. Sample weights are provided to account for subgroup oversampling and nonresponse in the NHANES cycle. To account for the NHANES analytic subsample (having at least 4 valid wear days of accelerometer monitoring), sample weights were recalculated from the publicly available NHANES sample weights to account for this additional sampling stage ( gov/nhanes_pam/reweight.html) (15). NHANES descriptive statistics (mean SD, median and interquartile range [IQR], and proportions with associated 95% confidence interval [95% CI]) used the recalculated weights for the analytic subsample. The OAI descriptive analyses used unweighted observed data. Due to different NHANES and OAI sampling procedures, we were unable to traditionally adjust for potential confounders. Therefore, sensitivity analyses were conducted that identified matched NHANES/OAI pairs using the following criteria: age ( 2.5 years), BMI ( 2.5 kg/m 2 ), sex, and post high school education (none versus at least some). From the matched pairs, we compared the time spent in MVPA between the OAI and the NHANES, using generalized estimating equations, controlling for lower-quarter pain and the interaction between group and lower-quarter pain. RESULTS In general, the sample of people with symptomatic knee OA was 54% women, with an average age of 65.5 years

4 Physical Activity in Adults With and Without Symptomatic Knee OA 1451 (95% CI 64.7, 66.3) and average BMI of 29.7 kg/m 2 (95% CI 29.2, 30.1). The general population sample without OA or knee pain was 45% women, with an average age of 63.0 years (95% CI 61.6, 64.4) and average BMI of 27.4 kg/m 2 (95% CI 26.9, 28.1). The demographics are further described by sex and age group in Table 1. Time spent in MVPA was low and similar in people with symptomatic knee OA compared with the general US population within age- and sex-specific strata. People with symptomatic knee OA spent 1 24 minutes/day in MVPA (median), while the general population spent 1 22 minutes/day in MVPA (Figure 2). In both groups, time spent Table 1. Demographics stratified by sex and age group for people with symptomatic knee OA (OAI) and for the general population without OA or knee symptoms (NHANES)* Men, ages Women, ages Demographics Total no. Symptomatic knee OA General Age, mean (95% CI) years Symptomatic knee OA 55.6 (55.0, 56.2) 64.0 (63.3, 64.7) 74.3 (73.7, 75.0) 81.3 (80.5, 82.1) 55.0 (54.4, 55.6) 64.8 (64.3, 65.4) 74.2 (73.5, 74.8) 81.8 (81.2, 82.4) General 53.5 (52.7, 54.3) 64.6 (63.3, 66.0) 74.5 (72.7, 74.8) 83.5 (83.2, 83.9) 53.2 (52.1, 54.2) 62.9 (62.3, 63.6) 73.8 (72.7, 74.8) BMI, mean (95% CI) kg/m 2 Symptomatic knee OA (29.3, 31.1) (29.1, 30.8) (27.8, 29.8) (23.9, 30.9) (29.5, 32.3) (30.0, 32.2) (26.7, 28.9) General (27.0, 28.9) (27.6, 29.6) (26.0, 28.9) (24.5, 25.9) (25.3, 28.0) (25.8, 28.4) (26.0, 28.9) Education, % Symptomatic knee OA <High school High school graduate Some college College graduate General <High school High school graduate Some college College graduate Race, % Symptomatic knee OA White African American Other General White African American Other Married, % Symptomatic knee OA General Income <$25,000, % Symptomatic knee OA General Comorbidity, % Symptomatic knee OA General Wear time, mean (95% CI) minutes/day Symptomatic knee OA 14.3 (14.0, 14.7) General 14.5 (14.1, 14.8) 14.1 (13.8, 14.4) 14.5 (14.1, 14.9) 13.4 (13.1, 13.7) 13.9 (13.3, 14.5) 12.9 (11.8, 13.9) 13.5 (12.4, 14.7) 14.7 (14.4, 15.0) 14.5 (13.9, 15.0) 14.0 (13.8, 14.8) 14.1 (13.6, 14.6) 13.4 (13.2, 13.7) 14.0 (13.4, 14.5) 82.6 (82.2, 83.1) 26.2 (23.8, 28.5) 26.6 (25.8, 27.5) 14.1 (13.3, 14.9) 13.9 (13.4, 14.4) * OA = osteoarthritis; OAI = Osteoarthritis Initiative; OA = osteoarthritis; NHANES = National Health and Nutrition Examination Survey; 95% CI = 95% confidence interval; BMI = body mass index.

5 1452 Thoma et al Figure 2. Median minutes per day (interquartile range [IQR]) in moderate-to-vigorous physical activity for people with symptomatic knee osteoarthritis (SxOA; from the Osteoarthritis Initiative) and the general population without osteoarthritis or knee symptoms (from the National Health and Nutrition Examination Survey). in MVPA decreased as age increased, and was generally higher in men compared to women. For our sensitivity analyses, the matching criteria produced 212 matches. Within each subsample, the median time spent in MVPA was 10.8 (IQR ) minutes/day in those with symptomatic knee OA and 8.0 (IQR ) minutes/day in the general population (Figure 3). Time spent in MVPA was log-transformed for the analysis due to a skewed distribution. People with symptomatic knee OA spent 28% (95% CI 6, 54) more time in MVPA than the general population without OA or knee pain (P = 0.009). While a significant difference was found between the matched groups, this difference was attenuated by controlling for differences in education (12% difference [95% CI 7, 36]; P = 0.26). The interaction between group and lower-quarter pain was not significant and therefore removed from the model. have been observed in the last 20 years (25), and the proportion of people who meet physical activity guidelines remains low. If people in the general population acquire physical activity from normal activities of daily life, it is not surprising that people with symptomatic knee OA also exhibit at least this level of physical activity. Continued efforts are needed to design and implement national programs to successfully increase leisure-time physical activity, regardless of the presence of knee symptoms. Our sensitivity analysis further supported the findings of low amounts of MVPA among people with symptomatic knee OA and the general population with OA or knee symptoms. In the sensitivity analysis, we identified pairs from each sample matched for age, sex, BMI, and post high school education, and controlled for the presence of other lower-quarter pain. In this constrained analysis, both adults with symptomatic knee OA and matched adults not reporting knee symptoms accumulated low levels of MVPA (median 10.8 versus 8.0 minutes/day) (Figure 3). Although the group difference was statistically significant when controlling for lower-quarter pain, the magnitude was small (<3-minute difference) and likely not clinically meaningful in the context of a 1,440-minute day. Despite matching for post high school education, this matching may not adequately address differences in education level (see education demographics in Table 1). In further analyses, group differences in physical activity were largely explained by explicitly controlling for differences in education levels between the matched samples, using education as a 4-level covariate as indicated by the categories in Table 1. These findings support the observation that adults with symptomatic knee OA had similar levels of MVPA to the general population without OA or knee symptoms. DISCUSSION We observed that people with symptomatic knee OA and those in the general population accumulate similarly low amounts of objectively determined MVPA. This observation was consistently held between people with symptomatic knee OA and those from the general population for both men and women across the age ranges (Figure 1). The low levels of MVPA in people with knee OA and adults from the general population that were observed in this study were not surprising. Contemporary studies consistently show a high prevalence of physical inactivity in the US (15,24). Despite national campaigns and increasing attention to the consequences of physical inactivity, only modest improvements in physical activity participation Figure 3. Median minutes per day (interquartile range [IQR]) in moderate-to-vigorous physical activity for matched cohort for the sensitivity analysis. People with symptomatic knee osteoarthritis (SxOA, n = 212) were matched by age, body mass index, sex, and college attendance to the general population without osteoarthritis or knee symptoms (n = 212).

6 Physical Activity in Adults With and Without Symptomatic Knee OA 1453 The current study clarifies conflicting reports from previous studies regarding the physical activity level of people with symptomatic knee OA relative to people in the general population without OA or knee symptoms. Smaller studies have reported lower levels of physical activity in people with knee OA compared to a healthy control group (11 13). Conversely, previous studies using larger cohorts of people with knee OA (5,7,8,14) reported a similar prevalence of meeting 2008 national physical activity guidelines using accelerometer-determined physical activity relative to reports from population-based studies (10,15). Similarly, a systematic review and meta-analysis by Wallis et al (14) also noted that 59 87% of adults with knee OA fail to meet physical activity guidelines, which was consistent with findings in the general population (15). Our study improves upon the current literature by directly comparing time spent in MVPA in people with symptomatic knee OA to people without knee symptoms or OA using large data sets. Modifiable barriers to participating in physical activity are similar in older adults with and without knee OA (26 28). Common barriers that emerge from qualitative studies include physical limitations (i.e., pain severity, comorbidities, concerns for injury), social influences (i.e., lack of spousal support, lack of encouragement from others, anxiety), personal beliefs of benefits (i.e., no perceived benefits, ineffective, poor self-confidence), and environment (i.e., built environment, weather, affordability) (26 28). Facilitators to physical activity participation are also similar among older adults with and without knee OA, including education regarding benefits and modes of physical activity, encouragement from physical therapists and physicians, positive self-image and self-confidence, ease of accessibility, and good social support (26 28). While these qualitative studies provide a rich understanding regarding barriers and facilitators to physical activity, our understanding of the extent to which these factors indeed impact physical activity participation are limited. For example, people with knee OA perceive pain to be a barrier to physical activity (1). Although the current study lacked data from the NHANES to evaluate the impact of knee-pain severity on physical activity levels, a study by White et al (8) observed that the proportions of people who met the 2008 Physical Activity Guidelines did not differ based on the presence of radiographic OA, or based on knee pain severity. Taken together, these studies suggest that pain itself may be a perceived barrier, but potentially not the primary barrier to general levels of physical activity. Our study has several limitations. As stated earlier, the 2 study samples employed different ActiGraph models. The primary discordance between the 2 models was in measuring slow walking (23). Thus, we only compared physical activity metrics that reflected MVPA, to avoid inconsistencies due to the ActiGraph model. Another limitation of the ActiGraph assessment of physical activity is that it does not include time in nonambulatory physical activity, such as swimming or cycling. However, walking is the primary mode of MVPA for older adults (3), and thus we do not expect that this limitation would alter the conclusions of this study. Notably, the NHANES is not a norm-referenced sample, and thus does not necessarily reflect a sample of healthy people. To reflect the general US population, the NHANES sample includes people with comorbidities or other chronic diseases (29). Thus, concluding that people with OA have similar levels of physical activity as healthy adults per se is not appropriate. There is some indication that the sample from the NHANES was particularly inactive (10,30), and that adults in the US may have increased physical activity levels between (when NHANES data were collected) and (when the OAI data were collected) (10). Despite these potential differences, rates of physical inactivity remain high, thus we do not expect that the general conclusions of this study would change (10). People with symptomatic knee OA and in the general population without OA or knee symptoms do little of the recommended MVPA. The results of this study reiterate the need for successful interventions to increase physical activity in the general population, as well as in people with knee OA. AUTHOR CONTRIBUTIONS All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be submitted for publication. Dr. White had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study conception and design. Thoma, Dunlop, Song, Lee, Tudor-Locke, White. Acquisition of data. Dunlop, Song. Analysis and interpretation of data. Thoma, Dunlop, Song, Lee, Tudor-Locke, Aguiar, Master, Christiansen, White. REFERENCES 1. Gyurcsik NC, Brawley LR, Spink KS, Brittain DR, Fuller DL, Chad K. Physical activity in women with arthritis: examining perceived barriers and self-regulatory efficacy to cope. Arthritis Care Res (Hoboken) 2009;61: Abell JE, Hootman JM, Zack MM, Moriarty D, Helmick CG. Physical activity and health related quality of life among people with arthritis. J Epidemiol Community Health 2005; 59: Hootman JM, Macera CA, Ham SA, Helmick CG, Sniezek JE. Physical activity levels among the general US adult population and in adults with and without arthritis. Arthritis Care Res (Hoboken) 2003;49: Shih M, Hootman JM, Kruger J, Helmick CG. Physical activity in men and women with arthritis National Health Interview Survey, Am J Prev Med 2006;30: Farr JN, Going SB, Lohman TG, Rankin L, Kasle S, Cornett M, et al. Physical activity levels in patients with early knee osteoarthritis measured by accelerometry. Arthritis Care Res (Hoboken) 2008;59: Herbolsheimer F, Schaap LA, Edwards MH, Maggi S, Otero A, Timmermans EJ, et al. Physical activity patterns among older adults with and without knee osteoarthritis in six European countries. Arthritis Care Res (Hoboken) 2016;68: Dunlop DD, Song J, Semanik PA, Chang RW, Sharma L, Bathon JM, et al. Objective physical activity measurement in the Osteoarthritis Initiative: are guidelines being met? Arthritis Rheum 2011;63: White DK, Tudor-Locke C, Felson DT, Gross KD, Niu J, Nevitt M, et al. Do radiographic disease and pain account for why people with or at high risk of knee osteoarthritis do not meet physical activity guidelines? Arthritis Rheum 2013;65: Freedson PS, Melanson E, Sirard J. Calibration of the Computer Science and Applications, Inc. accelerometer. Med Sci Sports Exer 1998;30:

7 1454 Thoma et al 10. Tucker JM, Welk GJ, Beyler NK. Physical activity in U.S. adults: compliance with the physical activity guidelines for Americans. Am J Prev Med 2011;40: Watanabe H, Urabe K, Takahira N, Ikeda N, Fujita M, Obara S, et al. Quality of life, knee function, and physical activity in Japanese elderly women with early-stage knee osteoarthritis. J Orthop Surg (Hong Kong) 2010;18: Winter CC, Brandes M, M uller C, Schubert T, Ringling M, Hillmann A, et al. Walking ability during daily life in patients with osteoarthritis of the knee or the hip and lumbar spinal stenosis: a cross sectional study. BMC Musculoskelet Disord 2010;11: Brandes M, Schomaker R, M ollenhoff G, Rosenbaum D. Quantity versus quality of gait and quality of life in patients with osteoarthritis. Gait Posture 2008;28: Wallis JA, Webster KE, Levinger P, Taylor NF. What proportion of people with hip and knee osteoarthritis meet physical activity guidelines? A systematic review and metaanalysis. Osteoarthritis Cartilage 2013;21: Troiano RP, Berrigan D, Dodd KW, M^asse LC, Tilert T, Mcdowell M. Physical activity in the United States measured by accelerometer. Med Sci Sports Exer 2008;40: Li J, Siegrist J. Physical activity and risk of cardiovascular disease: a meta-analysis of prospective cohort studies. Int J Environ Res Public Health 2012;9: Sluik D, Buijsse B, Muckelbauer R, Kaaks R, Teucher B, Johnsen NF, et al. Physical activity and mortality in individuals with diabetes mellitus: a prospective study and metaanalysis. Arch Intern Med 2012;172: Wilmot EG, Edwardson CL, Achana FA, Davies MJ, Gorely T, Gray LJ, et al. Sedentary time in adults and the association with diabetes, cardiovascular disease and death: systematic review and meta-analysis. Diabetologia 2012;55: Biswas A, Oh PI, Faulkner GE, Bajaj RR, Silver MA, Mitchell MS, et al. Sedentary time and its association with risk for disease incidence, mortality, and hospitalization in adults: a systematic review and meta-analysis. Ann Intern Med 2015;162: Moore SC, Lee I, Weiderpass E, Campbell PT, Sampson JN, Kitahara CM, et al. Association of leisure-time physical activity with risk of 26 types of cancer in 1.44 million adults. JAMA. Intern Med 2016;176: Lee IM, Shiroma EJ, Lobelo F, Puska P, Blair SN, Katzmarzyk PT. Effect of physical inactivity on major noncommunicable diseases worldwide: an analysis of burden of disease and life expectancy. Lancet 2012;380: Physical Activity Guidelines Advisory Committee report, To the Secretary of Health and Human Services. Part A: executive summary. Nutr Rev 2009;67(67): Kozey SL, Staudenmayer JW, Troiano RP, Freedson PS. A comparison of the ActiGraph 7164 and the ActiGraph GT1M during self-paced locomotion. Med Sci Sports Exer 2010;42: Hallal PC, Andersen LB, Bull FC, Guthold R, Haskell W, Ekelund U. Global physical activity levels: surveillance progress, pitfalls, and prospects. Lancet 2012;380: Keadle SK, McKinnon R, Graubard BI, Troiano RP. Prevalence and trends in physical activity among older adults in the United States: a comparison across three national surveys. Prev Med 2016;89: Franco MR, Tong A, Howard K, Sherrington C, Ferreira PH, Pinto RZ, et al. Older people s perspectives on participation in physical activity: a systematic review and thematic synthesis of qualitative literature. Br J Sports Med 2015;49: Petursdottir U, Arnadottir SA, Halldorsdottir S. Facilitators and barriers to exercising among people with osteoarthritis: a phenomenological study. Phys Ther 2010;90: Dobson F, Bennell KL, French SD, Nicolson PJ, Klaasman RN, Holden MA, et al. Barriers and facilitators to exercise participation in people with hip and/or knee osteoarthritis: synthesis of the literature using behavior change theory. Am J Phys Med Rehabil 2016;95: Song MR, Lee YS, Baek JD, Miller M. Physical activity status in adults with depression in the National Health and Nutrition Examination Survey, Public Health Nurs 2012;29: Berkemeyer K, Wijndaele K, White T, Cooper AJ, Luben R, Westgate K, et al. The descriptive epidemiology of accelerometer-measured physical activity in older adults. Int J Behav Nutr Phys Act 2016;13:2.